Individual and Combined Effects of Legacy and Emerging Contaminants on the Blue Crab Callinectes sapidus: Mercury and Bisphenol S as a Case Study

This study investigated the individual and combined effects of mercury (as HgCl2) and Bisphenol S (BPS) on the blue crab Callinectes sapidus, focusing on biomarkers measured in hemolymph, gills, and hepatopancreas and ultrastructure (transmission electron microscopy, TEM) observations. Adult males were exposed for seven days to environmentally relevant concentrations of each contaminant, alone and in mixture. Results revealed clear tissue-specific responses. In hemolymph, both contaminants reduced total hemocyte count and affected immune-related parameters, including hemocyte proliferation and enzymatic activities. In gills, mercury significantly decreased total antioxidant capacity, while both contaminants increased lipid peroxidation, indicating oxidative stress. BPS and the mixture stimulated catalase activity, whereas electron transport system activity increased only under combined exposure. In contrast, the hepatopancreas showed limited biochemical alterations, suggesting a higher resilience to medium-term exposure. TEM observations revealed a general decrease in granularity of hemocytes from crabs exposed to BPS and mixture, suggesting cell degranulation. In addition, infiltration of hemocytes into gills was observed in crabs exposed to experimental conditions, suggesting migration of hemocytes from hemolymph to peripheral tissues, while alterations of the microvilli arrangement were detected in digestive cells of BPS-treated crabs. Overall, the findings suggested that hemolymph and gills were more sensitive to contaminant exposure, while the hepatopancreas appears more resistant, at least under the experimental conditions tested. The study also suggests potential non-additive interactions between mercury and BPS.